Apparatuses consistent with the present invention relate to a measuring device, and more particularly to a measuring device having a replaceable sensor with a permanently connected signal cable and a connector at the cable end for transmitting a sensor signal. The measuring device further includes a non-volatile electronic data memory for holding sensor-specific calibration data, and an evaluation unit with a port for connecting the signal cable. The sensor signal is evaluated in the evaluation unit using the calibration data.
In measuring devices with replaceable sensors, the respective sensor can be easily decoupled from the evaluation unit by a pin-and-socket connector. In case of a defect, which occurs most often on the sensor, but may also occur in the evaluation unit, these components can be easily decoupled and replaced by an intact component to perform a repair. When different sensors with different metrological characteristics, such as different measured quantities or measurement ranges, are used, the sensors can be replaced while using the same evaluation unit. In this case, the evaluation unit is adapted to the changed metrological characteristics of the sensor by corresponding settings. The drawback in measuring devices of this type, however, is that after every replacement of a component, particularly a sensor, the entire measuring device must be recalibrated and the result stored in the form of calibration data, usually in a data memory of the evaluation unit or a personal computer connected downstream. This is not only very time consuming and expensive but has also the drawback that the respective sensor is not safely linked to the associated calibration data. This may lead to mistakes or even the loss of calibration data regarding the sensor.
To assign identification data to a sensor of a measuring device, a data plate with a readable code is typically mounted to the sensor itself or to a component permanently connected to the sensor, such as a connection cable. For example, the German Laid Open Publication DE 37 09 717 A1 and the German Utility Model DE 83 21 954 U1 each disclose a balance (measuring device) comprising a load cell (sensor) with a permanently connected signal cable and a connector at the cable end, a display unit with an indicator field (display), and a port to connect the signal cable. A data plate with readable metrological characteristics, such as the measuring range of the load cell, information as to the date of the last official calibration, and the validity of the calibration, is inseparably fixed to the signal cable, such that the data plate is in the immediate proximity of the display of the evaluation unit when the load cell is connected and the metrological characteristics can be read as required. The drawback is that this does not ensure a reliable assignment of the respective calibration data to a given replaceable load cell. A further drawback is that a manufacturer-specific connection is required, so that it is not possible to use sensors from just any manufacturer.
From the product descriptions of Dallas Semiconductor, a measuring device is known which has a replaceable sensor with a permanently connected signal cable and a connector at the cable end, and an evaluation unit with a port for connecting the signal cable. A data memory in the form of an EPROM or EEPROM, in which sensor-specific calibration data of the sensor are stored, is disposed within the connector. This provides a relatively safe assignment of the calibration data to the sensor and simple handling by means of the common pin-and-socket connector, but requires a manufacturer-specific probe with a special connector. Arranging the data memory within the connector furthermore has the drawback that the data memory can be damaged or tampered with if the connector is open. In addition, the spatial proximity of the data memory and the associated data lines to the signal lines of the signal cable within the connector may result in an electromagnetic interaction, so that the sensor signals and/or calibration data may be corrupted during signal or data transmission.